1. Field of the Invention
This invention relates to a bi-loop heat recovery system for a conventional oil-fired heating system, and particularly to a heating system of the type suitable for heating a dwelling or other enclosure.
2. State of the Art
In conventional heating systems, air from the enclosure to be heated provides oxygen for combustion; and when the system is in operation, products of combustion together with any excess air are exhausted through a stack or other vent to the atmosphere. The air which is drawn into the furnace for combustion purposes and then discharges to the atmosphere must, of course, be replaced in the enclosure; and in conventional systems this takes place by the drawing of cold outside air through the most permeable portions of the structure of the enclosure, namely, gaps around window sashes, doors, down fireplace flues and the like. Even when such a system is not in operation, heated house air continues to be discharged through the stack because of buoyancy (differential temperature) and a venturi effect (suction) caused by wind across the stack which induces drafts into the enclosure. The passage of air often creates palpable drafts or cold spots. Moreover, since an entire building's heated (moist) air can be drawn through the furnace and exhausted to the atmosphere at rates ranging and at times exceeding 1-2 ft. .sup.3 /sec., considerable heat and moisture losses are characteristic of conventional systems of the above-described type. Furthermore, in an effort to save energy individuals are insulating their homes and closing off all drafts and air leaks. All fuel-burning appliances need air in order to burn the fuel properly. If a furnace is "starved" of its necessary intake air, it will operate inefficiently.
It has therefore been proposed that heat losses can be reduced in heating systems by supplying fresh air to the return air stream. For example, in U.S. Pat. No. 2,962,218, issued Nov. 29, 1960, to Dibert, it was suggested that a preheated stream of cool external air be used to equalize the air pressure within the enclosure with outside atmospheric pressure, for a resultant reduction in seepage of external air. Similarly, in U.S. Pat. No. 1,726,727, issued Sept. 3, 1929, to Wood, a furnace is proposed in which fresh air may be preheated and then mixed with a supply stream drawn from return air.
It should be understood that conventional heating systems can produce toxic carbon monoxide which represents a serious health risk. In particular, if the flue of a conventional furnace becomes blocked, the products of combustion, which can include carbon monoxide, can flow into the living space. Other malfunctions of a furnace can also result in carbon monoxide entering the living space. The severity of this and other furnace operating hazards has been recognized by the United States Consumer Product Safety Commission which found that between July, 1975, and July, 1976, an estimated 426 deaths were caused by carbon monoxide poisoning due to furnace malfunctions. In the past the only practical solution to this problem has been to insure that a furnace is properly operated and maintained.